Antibodies to the class 2/3 OMPs (PorB) are bactericidal and antigenic diversity between these proteins forms the basis of the current serotyping classification. A PorB variable region (VR) typing method and and PCR method amplifying porB directly from cerebrospinal fluid were developed previously in our laboratory. Evaluation of an unusual Chilean strain (501) identified the strain as a hybrid type4, type 15 strain and subsequent rabbit immunization studies using this strain revealed immunodominance of individual epitopes corresponding to particular variable regions of the porin protein.